Most midsize to large computer systems have multiple printed circuit boards which must be electrically interconnected and compactly packaged. A typical such system has a "backpanel" which is a multilayered panel with certain layers having interconnecting conductors and other layers providing power and ground connections. It is known to connect each printed circuit board to the backpanel with a connector. The connector is attached to one end of the board and has a plurality of pins electrically connected to and extending away from the board. The pins are arranged in a matrix with multiple rows. For example, a connector may have its pins arranged in forty rows with three pins per row. The backpanel has circuit board to be mounted thereon. The pins extend through the holes in the backpanel making contact with selected conductors in the backpanel.
Printed circuit boards are normally positioned side-by-side with minimal clearance therebetween for compact packaging and reduced path lengths for electrical signals. This close spacing of boards mounted to the backpanel does not lend itself to modifications of the printed circuit boards that may produce lateral projections therefrom. For example, the cryogenic cooling of selected board components is impractical in the narrow confines between adjacent boards.
The close spacing of boards creates a diagnostic dilemma as well. In the past, boards that needed to be tested during operation would be unplugged from the backpanel and an extender board inserted between it and the backpanel so that individual board components could be monitored and tested. However, with ever increasing system speeds these extender boards create time delays by virtue of increased path lengths. This complicates component evaluation.